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Introduction to PsychToolbox in MATLAB

Introduction to PsychToolbox in MATLAB

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Introduction to PsychToolbox in MATLAB

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  1. Introduction to PsychToolbox in MATLAB Psych 599, Summer 2013 Jonas Kaplan, Ph.D. University of Southern California Week 5

  2. Week 4 Recap

  3. Drawing text • Two steps to drawing text: • 1. Set up all the properties of the text we want to draw (font, size, style) using separate commands • 2. Draw the text using DrawText

  4. Drawing Text Screen('DrawText',wPtr,text,x,y,color)

  5. Drawing Formatted Text DrawFormattedText(wPtr,textString,sx,sy,color,wrapat,flipHorizontal,flipVertical, vSpacing, rightoleft, winRect) Advantages over DrawText: Helpful for splitting text into multiple lines. Can include newline characters in the text string (\n). Can do automatic centering if you set sx to "center" or right justify if you set to "right"

  6. Images

  7. Displaying pictures • Steps to displaying a picture: • 1. Use imread() to read the image into a matrix of numbers • 2. Use MakeTexture to create an OpenGL texture using that matrix • 3. Use DrawTexture to draw the texture to the screen

  8. Images A = imread('mypicture.jpg'); [A, map] = imread('mypicture.jpg'); [A, map, alpha] = imread('mypicture.jpg');

  9. Images myTextureIndex = Screen('MakeTexture',wPtr, imageMatrix)

  10. Drawing Images Screen('DrawTexture', windowPointer, texturePointer [,sourceRect] [,destinationRect] [,rotationAngle] [, filterMode] [, globalAlpha] [, modulateColor] [, textureShader] [, specialFlags] [, auxParameters]); rect defining subpart of picture to present, default is whole picture rect defining subpart of screen to present picture in (defaults to center of screen)

  11. Positioning images 0,0 xOffset, yOffset xOffset + imageWidth, yOffset + imageHeight

  12. Scaling images • To scale an image, change the size of the destination rectangle

  13. Rotating images Screen('DrawTexture', windowPointer, texturePointer [,sourceRect] [,destinationRect] [,rotationAngle] [, filterMode] [, globalAlpha] [, modulateColor] [, textureShader] [, specialFlags] [, auxParameters]); set rotation angle. upright image is 0 degrees

  14. Multiple images • You can draw multiple image textures to the back buffer, and then flip to show them at the same time

  15. Movies • 1. OpenMovie to open the movie file • 2. PlayMovie to start playing • 3. Loop: • GetMovieImage to create frame texture • Draw texture and flip screen • 4. PlayMovie to stop playing • 5. CloseMovie to close movie file

  16. Movies http://www.gstreamer.com

  17. Assignment # 4 • Create a function called yourInitials_week4() • The function should take one input: • subjectCode, a string identifying the subject • The function should do the following: • Using a loop, present 20 trials of the following emotion categorization experiment. On each trial, a picture will appear. The picture will randomly be chosen between sad.jpg and angry.jpg. The location of the picture will also be randomly chosen between the left and right side of the screen. The edge of the picture should always be 100 pixels from the center of the screen, horizontally. • Once the picture appears, wait for the user to press a key. The subject should press S for sad and A for angry. • On each trial, write out the following information to the next line of a log file. The log file should be named subjectCode_log.txt where subjectCode is the code that they entered from the command line. Each line should contain: the trial number, which picture was presented, where it was presented, which key was pressed, the reaction time, and whether or not the keypress was correct. • When the experiment is over, print out the subject's overall accuracy to the command window.

  18. Week 5 • Sound • Collecting input: keyboard, mouse, joystick, etc. • Sending output: external devices

  19. Sound • Creating sounds to play • Playing existing sound files

  20. Sound • PsychPortAudio is the sound driver for PTB-3 • Type PsychPortAudio in the command window to see all of the subcommands, just like Screen • Get help on a subcommand just like Screen:PsychPortAudio Start? • Test your audio setup with BasicSoundOutputDemo

  21. Sound data • Sound data should be in the form of a matrix where each row is one sound channel • Samples in the vector should range from -1 to 1, where 0 is silent. • You can create a sound by generating data for a matrix on your own, or you can read in from a wav file

  22. Reading from wav files Y = wavread(FILE) [ Y, freq ] = wavread(FILE)

  23. Reading from .au files Y = auread(AUFILE) [Y, freq ] = auread(AUFILE)

  24. Reading from audiofiles [Y, freq ] = audioread() New Matlab command available in versions 2012b and later, will read many audio formats including WAV, FLAC, MP3, MPEG-4, OGG

  25. Reading in sounds >> PsychtoolboxRoot ans = /Applications/Psychtoolbox/ >> cd /Applications/Psychtoolbox/PsychDemos/SoundFiles >> ls COPYING motor_a8.wav phaser.wav funk.wav motor_b8.wav radar.wav >> [funkData, funkFreq ] = wavread('funk.wav'); >> funkFreq funkFreq = 48000 >> whosfunkData Name Size Bytes Class Attributes funkData 624000x1 4992000 double >> plot(funkData)

  26. Reading in sounds

  27. Preparing sound data for playing >> whosfunkData Name Size Bytes Class Attributes funkData 624000x1 4992000 double >> funkData = funkData' >> funkData = [funkData; funkData]; >> whosfunkData Name Size Bytes Class Attributes funkData 2x624000 9984000 double change column to row duplicate to make two rows for stereo

  28. Creating sound stimuli • Length of vector is sampling frequency * duration (we want sfreq samples per second for X seconds )

  29. Creating sounds >> samplingFreq = 48000; >> duration = 5; >> whitenoise = rand(1,(samplingFreq * duration)); >> whoswhitenoise Name Size Bytes Class Attributes whitenoise 1x240000 1920000 double

  30. Creating sounds • MakeBeep() will create a pure tone • Y = MakeBeep( freq, duration, samplingrate)

  31. Creating sounds >> beep1000 = MakeBeep(1000,5,48000); >> sound(beep1000,48000); >> beep500 = MakeBeep(500,5,48000); >> sound(beep500,48000); matlab's built-in sound function, not PTB's

  32. Steps to playing a sound • InitializePsychSound • open audio channel with PsychPortAudio('Open') • fill audio buffer with PsychPortAudio('FillBuffer') • start playing a sound with PsychPortAudio('Start') • stop playing a sound with PsychPortAurio('Stop') • close the audio channel with PsychPortAudio('Close')

  33. Step 1: Intialize • InitializePsychSound • Loads the sound driver. Place this at the beginning of your script. • on Windows, things may not work with high precision timing without an ASIO sound card (read help InitializePsychSound if you are on Windows)

  34. Step 2: Open audio channel pahandle = PsychPortAudio('Open' [, deviceid][, mode] [, reqlatencyclass][, freq][, channels] [, buffersize] [, suggestedLatency][, selectchannels][, specialFlags=0]); playback channels: 1 = mono 2 = stereo etc. default is 2 how aggressively to take over the sound device in order to assure latency requested playback rate in Hz

  35. Step 3: Fill the audio buffer PsychPortAudio('FillBuffer', pahandle, bufferdata); This is analogous to drawing on the back buffer with the Screen command. We fill the buffer now, but it will not be heard until we play it.

  36. Step 4: Start playback startTime = PsychPortAudio('Start', pahandle [, repetitions=1] [, when=0] [, waitForStart=0] [, stopTime=inf] [, resume=0]); Wait until this time to start playing (default is play now) Set to 0 to repeat indefinitely set a time to stop playing 0: Ask playback to start and move on 1: wait for playback to actually begin. A 1 here is necessary if you want to get timing info back

  37. Remaining steps • Stop playback if necessary: PsychPortAudio('Stop',pahandle); • Close the audio driver:PsychPortAudio('Close',pahandle);

  38. Sound recording • Also done through PsychPortAudio • See BasicSoundInputDemo.m

  39. Sound recording steps • Initialize sound driver: InitializePsychAudio • Open audio channel for recording with PsychPortAudio('Open') setting mode to 2 • Clear a buffer using PsychPortAudio('GetAudioData') • Start recording with PsychPortAudio('Start') • Stop recording with PsychPortAudio('Stop') • Get audio data using PsychPortAudio('GetAudioData')

  40. Step 2: Open audio channel pahandle = PsychPortAudio('Open' [, deviceid][, mode] [, reqlatencyclass][, freq][, channels] [, buffersize] [, suggestedLatency][, selectchannels][, specialFlags=0]); 1: sound playback only (default) 2: audio capture 3: simultaneous capture and playback (may not work on all hardware)

  41. GetAudioData [audiodataabsrecposition overflow cstarttime] = PsychPortAudio('GetAudioData', pahandle [, amountToAllocateSecs] [, minimumAmountToReturnSecs][, maximumAmountToReturnSecs] [, singleType=0]); Call before you start recording to setup an empty buffer, then after recording to retrieve recorded data

  42. Writing data to file wavwrite(audiodata, freq, nbits, filename) audiowrite(filename, audiodata, freq)

  43. Collecting responses